http://stackoverflow.com/questions/3903155/synchronous-query-to-web-sql-database

1.首先websql openDatabase（）方法打开数据库的其结果必然以异步方式返回结果，openDatabaseSync()方法可以同步方式打开数据库，但是貌似safari游览器中找不到这样的一个方法。

To get an object implementing DatabaseSync you have to call openDatabaseSync(...) instead ofopenDatabase(...). I don't know about the iPhone, or what the oDB object you have is, but according to spec you only get the openDatabaseSync method in a WebWorker and not in the normal web browser window. Certainly XMLHttpRequest has demonstrated that potentially-length synchronous operations in the UI thread are not a good idea.
 
2.看了老外的另外一个方案：http://stackoverflow.com/questions/3903155/synchronous-query-to-web-sql-database
发现其实可以直接写在回调函数中不必拆分成多个函数，这样就可以解决异步的问题了，如下（所有代码逻辑都在回调函数中完成）：

function getFolder(id, callback) {

          var data = [];

          ldb.transaction(function(tx) {

          tx.executeSql('SELECT * FROM folders where id=?', [id],

            function (tx, results) {

                if (results.rows && results.rows.length) {

                    for (i = 0; i < results.rows.length; i++) {

                        data.push(results.rows.item(i));

                    }

                }

                if( typeof(callback) == 'function') callback(data);

          },

          function(tx, error) {

              console.log(error);

          });

      });

}